The orbiting
Chandra X-ray Observatory observed Saturn for 20 hours in April 2003 to produce this false
colour image.

Image credit: NASA/CXC/SAO

For the first time, an unambiguous X-ray emission has been detected on Saturn
by a team from Hamburg University (Germany). The image obtained with the Chandra
X-ray Observatory clearly shows an X-ray emission that is concentrated near Saturn's
equator. This result was very unexpected in comparison to Jupiter's X-ray emission:
on Jupiter, X-ray emission is mainly concentrated near the poles and is related
to the auroral mechanism. The physical processes explaining Saturn's X-ray emission
are still unknown.

The Chandra X-ray Observatory is a space observatory dedicated to X-ray astronomy. Launched
on July 23rd, 1999, this X-ray telescope is particularly dedicated to the observation of
high-energy sources in the universe. It has also been used to study the following solar system
objects: the Moon, Venus, Mars, Jupiter, and even the Comet C/1999 S4 LINEAR.

Using Chandra, Jan-Uwe Ness and his colleagues detected an unambiguous X-ray emission from the
planet Saturn for the first time. A few years ago, a possible such emission was observed using
ROSAT, but the present detection is the first certain one.

Ness and his team observed Saturn in April 2003 for about 20 hours. The picture
above shows the X-ray image of Saturn that they obtained (in false colour). Each
colour (RGB) corresponds to a different energy range of the observed X-rays. Beyond
the X-ray detection from Saturn, this Chandra observation allowed the investigators
to perform the first in-depth analysis of this emission. The same team also detected
X-ray emissions from Saturn using the XMM-Newton Observatory. The observed signal
was very similar to what was found with Chandra.

Spectral analysis of the X-rays detected from Saturn with Chandra shows that
the signal looks remarkably like that of solar X-ray emissions. This indicates
that Saturn's X-ray emission originates from solar X-rays scattering in Saturn's
atmosphere, a result that is very surprising, as such a process has already been
studied on the Moon and was not expected to be so efficient on Saturn.

In addition to the scattering of solar X-rays, on Earth, X-rays are also produced by the same mechanism
that creates the aurorae in the polar regions. Aurorae are caused by solar wind electrons that enter the
Earth's atmosphere, thus resulting in these spectacular visible lights. At the same time, X-rays are also
produced. The same mechanism has been found to exist on Jupiter: Jovian aurorae have been detected in the
UV wavelengths, along with an associated X-ray emission. Saturn was also expected to emit X-rays in the
polar region, since spectacular polar aurorae have been observed in the UV wavelengths.

With Chandra, J.-U. Ness and his colleagues were able to study for the very
first time how the X-rays are distributed on Saturn's disc, in order to look for
polar X-ray emission. They found that the observed X-ray emission appears to be
concentrated around Saturn's equator. Surprisingly, no auroral X-ray emission
has been observed at all. However, the North Pole was occulted by Saturn's rings
and X-ray emission from northern polar regions may have been hidden.

Comparison between Saturn's and Jupiter's X-ray emissions shows that their X-ray production mechanisms are
very different. First of all, the spatial distribution differs: on Jupiter, X-rays are concentrated in polar
regions (see Chandra press release about Jupiter), suggesting that magnetic fields play an important role.
Such a polar X-ray emission has not been found on Saturn, but cannot be excluded. Secondly, the X-ray flux on
Saturn is significantly lower than that seen on Jupiter. Nonetheless, the emission level observed from Saturn
is consistent with the X-ray equatorial emission from Jupiter, indicating that both emissions originate from
similar processes. Ness and his colleagues point out that no single mechanism can easily account for the
observed emissions; therefore, they expect combined mechanisms to be involved.

Thanks to the high-angular resolution of the Chandra Observatory, the new detection of X-ray emissions from
Saturn, as well as recent results on the same subject from Jupiter, will allow for important progress in the
observations of X-rays on giant planets.

The PlanetsFrom tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets. GET YOUR COPY

Hubble RebornHubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts. GET YOUR COPY

3D UniverseWitness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D! GET YOUR COPY